Field of the Invention
The present invention relates to a vehicle transmission equipped with a rotary shaft and a plurality of speed change gears.
Description of Related Art
As a transmission used in an automotive vehicle such as a motorcycle, a constant mesh type multi-stage speed changing device is available such as disclosed in, for example, the Japanese Laid-open Patent Publication No. 2010-084917. Since a rotary shaft employed in such a speed changing device is formed integrally with speed change gears, spline serrations and others, the outer diameter of the rotary shaft is not constant and a large diameter portion and a reduced diameter portion are formed in the rotary shaft. Also, a plurality of speed change gears includes a fixed gear formed integrally with the rotary shaft, an engagement gear splined to the rotary shaft and a rotary gear mounted relatively rotatably on the rotary shaft.
In such speed changing device, in the event that the rotary gear is provided in the vicinity of the large diameter portion, when the rotary shaft rotates and the rotary gear run idle, an edge of an escapement (other end of the escapement) formed laterally of the rotary gear in an outer periphery of the rotary shaft strongly contacts an inner peripheral surface of the rotary gear. Additionally, a lubricant oil at this sliding portion becomes short, and therefore, friction induced sounds are apt to be generated between the rotary shaft and the rotary gear.
In order to suppress the friction induced sounds, the inventor of the present invention has made use of a tonic groove in the inner peripheral surface of the rotary gear to thereby increase the amount of lubricant at the sliding portion, which use has resulted in the effect of suppressing the generation of the friction induced sounds. This measure has, however, been found bringing about the reduction in contact surface area between the rotary gear and the rotary shaft and, therefore, the contact pressure poses a problem. It is also known that interposition of a tubular collar between the rotary gear and the rotary shaft to avoid the contact of the edge of the escapement with the inner peripheral surface of the rotary gear is effective to suppress the friction induced sounds. However, this countermeasure brings about an increase of the inner diameter of the rotary gear by a quantity corresponding to the interposition of the collar. Therefore, particularly where a dog transmission, for example, is used, a dog tooth is apt to be displaced radially outwardly, and accordingly, alteration of the transmission in its entirety may become required.